The present invention relates to a flat panel display device for compensating a threshold voltage of a panel; and, more particularly, to a flat panel display device capable of simplifying a circuit and a driving method, improving an opening ratio of a panel and enhancing an image quality of a display unit by compensating a panel threshold voltage through a driving circuit of the flat panel display device.
Generally, electroluminescence (hereinafter referred as to EL) is a phenomenon that a fluorescent substance luminesces as a current passes through it. An EL panel is typically used for illuminating light at the back of a liquid crystal display (hereinafter referred as to LCD) of a portable computer such as a notebook computer. However, since the EL panel is recently enabled with a function of self-luminescence, an additional backlight is not required compared to a conventional LCD. Based on this advantage and studies on such methods for acquiring a high definition image and a longer lifetime of the EL, the EL panel, in today, is employed for a high definition display unit including a LCD for a mobile telecommunication terminal. Furthermore, the EL panel will have broad applications in a near future. The EL panel includes an organic or inorganic self-luminescent body being placed in between two thin electrodes. Indeed, one of the two thin electrodes is transparent. This luminescence is caused by the energy released when excited electrons of a particular impurity at a central luminescence of a luminescent substance return to their ground states. Herein, free electrons accelerated by the EL excite the electrons of the particular impurity, which is also called an activator. Intensity of the luminescence increases in proportion to exp(xe2x88x92c/{square root over (xcexd)}), and frequency also increases proportionally up to a certain point.
The luminescence phenomenon due to an organic substance is discovered by Anthracene in 1960s. Thereafter, Eastman Kodak Company developed an ultra thin film double layer stacking type organic EL device in 1987, and Pioneer Corporation commercialized a single color organic EL display device by the end of 1997. A 5.5 inched natural color organic EL display device developed by Sanyo-Kodak is further demonstrated at the Society for Information Display(SID) in 2000.
The organic EL device has about 10 V of a driving voltage, which is lower than driving voltages of other display devices such as a thin film transistor-liquid crystal display (TFT-LCD), a plasma display panel (PDP), a field emission display (FED) and so forth. Also, the organic EL device has an advanced perceptibility due to self-luminescence. Furthermore, it is possible to make a thickness of the organic EL device thinner because it does not need a backlight unlike the TFT-LCD. Compared to currently used LCD, the organic EL device also has a rapid responsiveness and a wide angular field, and thus, it is expected to be a next generation display device.
FIG. 1 is a circuit diagram showing an organic EL display unit according to a prior art. The conventional organic EL display unit 100 includes a first TFT 101 having a first (source) terminal that receives a data signal from a source line and a second (gate) terminal that receives a gate enable signal from a gate enable line (GE), a second TFT 102 having a first (source) terminal supplied with power from a power line and a second (gate) terminal connected to a third (drain) terminal of the first TFT 101, a power maintenance capacitor 103 that charges a driving voltage of the second TFT 102 through which a first terminal is connected to the first terminal of the second TFT 102 and a second terminal to the third terminal of the first TFT 101, and an organic EL device 104 having a first terminal connected to a third (drain) terminal of the second TFT 102 and a second terminal is coupled to a ground terminal luminesces in case that currents are flowing.
The following will describe operations of the organic EL display unit 100 in accordance with the prior art.
Firstly, a gate enable signal provided from the gate enable line (GE) is activated, and the first TFT 101 is turned on. At this time, display data are transmitted to the second terminal of the second TFT 102 through the source line and the first TFT 101. This voltage is transmitted to the second TFT 102, which is a driving transistor, and the power maintenance capacitor 103 of the power line. Once the power maintenance capacitor 103 is charged with the driving voltage, the organic EL device 104 luminesces since currents can flow from the power line to the organic EL device 104. Even if the gate enable signal from the gate enable line (GE) is inactivated, the power maintenance capacitor 103 is still able to luminesce because the driving voltage for making the organic EL device 104 luminesce is still remained causes currents to flow from the power line to the organic EL device 104.
However, in case of driving the organic EL device 104 based on the above scheme, the second TFT 102 of each display unit cell has a different threshold voltage (Vth), and thus, an amount of currents supplied to the organic EL device 104 in each cell is different. Herein, the second TFT 102 is a driving transistor for the organic EL device 104. That is, there occur problems of a non-uniform screen and a decreased image quality because intensity of luminescent light of the organic EL device 104 changes inconsistently.
FIG. 2 is a circuit diagram showing a typical organic EL display unit 200 for coping with the inconsistent Vth according to another prior art. The typical organic EL display unit includes a first TFT 201 having a first (source) terminal that receives a data signal from a source line and a second (gate) terminal that receives a gate enable signal from a gate enable line (GE), a first capacitor 202 that charges a driving voltage of a second TFT 203 by being connected to a third (drain) terminal of the first TFT 201, the second TFT 203 having a first (source) terminal supplied with power from a power line and a second (gate) terminal connected to a second terminal of the first capacitor 202, a second capacitor 204 that charges a threshold voltage of the second TFT 203 through which a first terminal is connected to the first terminal of the second TFT 203 and a second terminal to the second terminal of the first capacitor 202, a third TET 205 having a first (source) terminal connected to the second terminal of the second TFT 203, a second (gate) terminal receiving a first switch control signal AZ and a third (drain) terminal connected to a third (drain) terminal of the second TFT 203, a fourth TFT 206 having a first (source) terminal connected to the third terminal of the third TFT 205 and a second (gate) terminal receiving a second switch control signal AZB and an organic EL device 207 that luminesces when currents are flowing through which a first terminal is connected to a third (drain) terminal of the fourth TFT 206 and a second terminal coupled to a ground terminal.
FIG. 3 is a diagram showing procedural timing for operating the organic EL display unit 200 according to still another prior art. With reference to the operational timing, the following will describe operations of the organic EL display unit 200 in accordance with the prior art.
Firstly, once a gate enable signal from the gate enable line GE is activated in a state that a second switch control signal AZB is precedently activated, the first switch control signal AZ is activated to primarily turn the second TFT 203 on, thereby charging a threshold voltage of the second TFT 203 connected to the second capacitor 204. Afterwards, the first switch control signal AZ is inactivated, and a driving voltage, i.e., DATA, of the second TFT 203 is transmitted from the source line to the first capacitor 202. Herein, the second TFT 203 is a driving transistor. Once the first capacitor 202 is charged with the driving voltage, the first capacitor 202 is supplied with the driving voltage that allows the organic EL device 207 to luminesce. At this time, the threshold voltage and the driving voltage of the second capacitor 204 drive the second TFT 203. Also, currents are set to flow from the power line to the organic EL device 207, which in turn, luminesces.
However, in the organic EL display unit 200 in accordance with the prior art, the number of periphery circuits for driving the cell also increases. Thus, an area for pure luminescence decreases, resulting in problems of decreasing an opening ratio and complicating the driving circuit since it is required to have more than 4 signal lines accompanying to an increase of control signals.
It is, therefore, an object of the present invention to provide a flat display panel device capable of simplifying a circuit and a driving method, enhancing particularly an image quality and increasing an opening ratio of a panel by compensating a panel threshold voltage when driving the flat panel display device.
In accordance with an aspect of the present invention, there is provided a flat display panel device for compensating a panel threshold voltage, including: a driving unit receiving a panel threshold voltage and outputting a driving signal, wherein the driving unit samples and charges the panel threshold voltage supplied from a source line and generates the driving signal from the panel threshold voltage charged therein when a displaying data are inputted thereto; and a displaying unit, wherein the displaying unit displays by driving a luminescent device therein with a gate enable signal from a gate enable line, a power from a power line and the driving signal from the driving unit, and supplies the panel threshold voltage to the driving unit by receiving a first switch control signal.